1. Field of the Invention
This invention relates to an automatic broadcast wave tuning device and, more particularly, to an automatic broadcast wave tuning device for a radio data system (hereinafter referred to as RDS) receiver to receive RDS data wherein the radio receiver is controlled to tune in a broadcast wave bearing RDS data transmitted by a broadcasting station.
2. Description of the Prior Art
As a well known radio service, a radio data system (RDS) is common in Europe for providing broadcast wave listeners with a radio service. In such RDS, informative data relating to broadcast programs are transmitted simultaneously with the broadcast programs in a multiplex modulation from broadcasting stations and, upon receiving the broadcast waves, a desired broadcast program is selected by a broadcast wave listener based on demodulated data.
The RDS is a data system standardized in the Europe Broadcasting Union (EBU), wherein the data relating to the broadcast such as broadcast programs and the like are coded into a two phase Differential Phase Shift Keying (DPSK) signal having a bit rate of 1187.5 bps, and these coded data are transmitted by frequency-modulating a sub-carrier in such that modulating a 57 KHz sub-carrier in accordance with a double-sideband carrier suppression amplitude modulation.
In the RDS, the whole data are transmitted as a unit which is called a group consisting of 104 bits. One group in turn consists of four blocks, each of which consists of 26 bits. The data contained in each group are prescribed depending on their locations, whereby 16 bits of the first block always designate a program identification code (PI code), while in the second block, the first 5 bits designate a group-type code, the next one bit designates a traffic-program identification code (TP code), and the next succeeding 5 bits designate a program type code (PTY code).
Further, the contents of the remaining are a traffic announcement identification code (TA code), program service name data (PS data) such as broadcasting station names, broadcasting network names and the like, and a list of alternative frequencies data (AF data) for identifying broadcasting network stations which broadcast the same program.
In a motor vehicle-mounted RDS receiver, a poor reception is quite often encountered while listening to a broadcast during a motor vehicle travel. However, in the RDS broadcast, since the AF data of the broadcasting stations within the same broadcasting network, which stations are broadcasting the same broadcast program on different frequencies, are available as described above, it is possible to tune in another broadcasting station within the same broadcasting network having a greater signal level, or a stronger electric field strength, than that of the broadcasting station presently tuned in based on the AF data stored in a memory for chasing the same broadcast program.
However, there has been a problem for causing faulty operation of the RDS receiver depending on a course of the motor vehicle such that the RDS receiver might come across a broadcasting station, out of but neighboring to the broadcasting network, having the AF data allocated to the same frequency as that of the broadcasting station within the broadcasting network, or the RDS receiver might tune in a wrong program as there are so-called non RDS broadcasting stations which are not capable of transmitting RDS data. This kind of faulty operation often happens when the motor vehicle is driven through many countries in Europe along the boundaries.
Further, wrong AF data may have been stored in a memory due to an unknown reason in a duration of demodulating the received RDS data and this results in a problem for causing improper selection in the automatic tuning operation. A prior-art-type automatic tuning device is disclosed, for example, in the patent application laid-open No. 2-105731.
It is therefore an object of this invention to eliminate the problems encountered by prior-art-type RDS receivers and to provide an automatic broadcast wave tuning device which is capable of preventing a RDS receiver from faulty operation.